Thermographic diazo-type copying paper

ABSTRACT

A thermographic diazo-type copying paper which is prepared by applying, onto a support, a mixed solution containing a diazo compound, a coupler, an acid stabilizer and a thermally decomposable salt which has an alkali-generating ability, and further containing thiourea or a derivative thereof and a metal sulfate, and then drying the same, is of a highly improved shelf life and also provides a clear copied image which is highly increased in color density.

United States Patent Takehiko lwaoka Tokyo;

Inventors Tomiaki Asami, Kanagawa, both of Japan Appl. No. Filed Patented Assignee THERMOGRAPHIC DIAZO-TYPE COPYING PAPER 2 Claims, No Drawings US. Cl 96/91, 96/49 Int. Cl G03c l/60 Field of Search 96/91, 75, 49

References Cited UNITED STATES PATENTS 3,248,220 4/1966 Van Rhijh 96/49 X 3,353,984 11/1967 Landau 96/75 X Primary Examiner-Norman G. Torchin Assistant Examiner-Charles L. Bowers, Jr. A ttorney Woodhams, Blanchard and Flynn ABSTRACT: A thermographic diazo-type copying paper which is prepared by applying, onto a support, a mixed solution containing a diazo compound, a coupler, an acid stabilizer and a thermally decomposable salt which has an alkaligenerating ability, and further containing thiourea or a derivative thereof and a metal sulfate, and then drying the same, is of a highly improved shelf life and also provides a clear copied image which is highly increased in color density.

THERMOGRAPI-IIC DIAZO-TYPE COPYING PAPER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is concerned with a diazo-type copying paper, and more particularly, it relates to a diazo-type copying paper which is adapted to produce a copied image through the mechanism of fonning an azodye by the application of heat. Still more particularly, the present invention relates to a thermographic copying paper which is capable of producing a copied image having a highly improved clarity and a highly increased color density owing to the inclusion, in the light-sensitive layer of this copying paper, thiourea or a derivative thereof and also a metal sulfate in addition to an alkali-generating agent.

2. Description of the Prior Art In general, a diazo-type copying paper designed for development by the application of heat is provided on one surface thereof with a light-sensitive layer which basically contains the following four components, i.e., a diazo compound a coupler, an acid stabilizer and a thermally decomposable alkali-generating agent. In view of the fact that this thermally decomposable alkali-generating agent is a component which directly participates in the reaction between the diazo compound and the coupler, it is no exaggeration to say that the quality of the thennographic copying paper per se is determined by the type of the alkali-generating agent which is adopted in the formation of the light-sensitive layer of the copying paper.

As the alkali-generating agents which have been used in the conventional thermographic copying papers, various thermally decomposable inorganic as well as organic salts such, for example, as the salts of metals and acids such as acetic acid and malonic acid, or the salts of lower alkylamines and acids such as acetic acid and malonic acid, are known. These salts, however, have drawbacks such as they possess a very limited ability of supplying alkali when they are used independently, and also that, even when they are used in large amounts in the light-sensitive layers of the thermographic copying papers, it is still impossible to obtain copied images having a highly improved clarity from such copying papers. Of all these salts, those thermally decomposable salts of alkali metals are especially poor in their ability of supplying alkali, and accordingly, they fail to give even the expected color tones of the couplers employed. In order to solve such problems, there has been made a proposal to use the aforesaid salts jointly with urea, derivatives thereat or acidamides. This proposal, however, had a great disadvantage in that the shelf life which is one of the most important properties of thermographic copying papers was sacrificed.

SUMMARY OF THE INVENTION It is, therefore, the object of the present invention to provide a thermographic copying paper which is capable of providing a copied image having a highly improved clarity and a highly increased color density without deterioration of the shelf life of the copying paper in the least by including, in the light-sensitive layer, at least one compound selected from the group of thiourea and derivatives thereof, in addition to such an inorganic or organic salt as has been described above which serves as a thermally decomposable alkali-generating agent, and further by including therein metal sulfate.

Briefly, the thermographic copying paper of the present invention is manufactured by applying, onto an appropriate support paper, a mixed solution which contains a diazo compound, a coupler, an acid stabilizer, an alkali-generating agent, a compound selected from the group consisting of thiourea and derivatives thereof, and also metal sulfate, and then by drying the same. When the thermographic copying paper thus manufactured is exposed to ultraviolet rays through an original placed on the light-sensitive layer thereof, the diazo compound located in the exposed areas of the lightsensitive layer undergoes photolysis, and as a result, there is formed a latent image in said areas of the light-sensitive layer. By bringing this exposed copying paper which carries this latent image into contact, for several seconds, with a hot roller having a surface heated to a temperature ranging from about C. to 200 C., the aforesaid salts are decomposed due to the applied heat so that alkali is generated. Due to the applied heat so that alkali is generated. Due to the action of this generated alkali, the diazo compound is caused to effect a coupling reaction with the coupler to thereby form an azodye. Thus, a clear copied image is developed.

The reason why in the present invention the combined use of thiourea or a derivative thereof and a metal sulfate bring forth various valuable advantages such as the improved shelf life of the copying paper and the improved clarity of the copied image, has not been elucidated yet. It may be considered, however, that the thiourea and the metal sulfate jointly form a very stable complex salt at normal temperature. lt may be presumed also that this complex salt is melted when placed under development conditions, of which the optimum condition is defined as conducting the development at C. for 6 seconds, and also that this melted complex salt accelerates the reaction between the diazo compound and the coupler.

The diazo compounds which can be applied to the present invention include almost all kinds of diazo compounds that have been employed in the manufacture of those two-component diazo-type photographic copying papers. The following compounds after being diazotized can also be used as the diazo compounds in the present invention. These diazo compounds are used normally in the form of a double salt of a diazo compound and a metal salt such as zinc chloride, tin chloride and cadmium chloride.

p-aminodiphenylamine N-B-hydroxyethyl-ethyl-p-phenylenediamine N-fi-hydroxyethyl-methyl-p-phenylendiamine p-ethlamino-m-toluidine p-dimethylaminoaniline p-diethylaminoaniline 4-benzoylamino-2,S-diethoxyaniline 4-morpholinoaniline and 4-morpholino-2,5-dimethoxyaniline.

As is the case with the aforesaid diazo compounds, the couplers which can be applied to the present invention are selected from those known couplers which have been employed in the manufacture of the conventional two-component diazotype photographic copying papers, and they in clude the following substances:

Resorcin Phloroglucin Acetoacetanilide 2, 3-dihydroxy-naphthalene--sodium sulfonate 2-naphthol-3,6-sodium disulfonate l-naphthol-4-sodium sulfonate 2,3,8-trihydroxy-naphthalene-6-sodium sulfonate, and

l-hydroxy-2-aminonaphthalene-3,6-sodium sulfonate Acid stabilizers, on the other hand, are used in the present invention in order to prevent the occurrence of a precoupling reaction between the diazo compounds and the couplers. As the acid stabilizers, those compounds which are stable at normal temperature are used in general. These acid stabilizers may be either inorganic compounds or organic compounds. Usually, such acids as tartaric acid, citric acid, boric acid, phosphoric acid and pyrophosphoric acid are used most widely.

The thermally decomposable alkali-generating agent which can be applied to the present invention consists of at least one compound selected from the group consisting of salts of metals or ammonium and acids such as halogenated acetic acid, halogenated malonic acid and cyanoacetic acid; and salts of alkylamines having one to four carbon atoms, guanidine or its derivatives and halogenated acetic acid or halogenated malonic acid and cyanoacetic acid. These alkali-generating agents are neutral salts and are adapted to be decomposed when they are heated at a temperature ranging from 100 C. to 200 C. for several seconds to produce alkali which serves to neutralize the acid stabilizer which is contained jointly in the light-sensitive layer, and at the same time it contributes to the acceleration of the coupling reaction which takes place between the diazo compound and the coupler.

The aforesaid metal salts which are used as the thermally decomposable alkali-generating agents include, for example, lithium salts, potassium salts and calcium salts. Whereas, guanidine derivatives include benzoylguanidine, biguanide, aminoguanidine, guanyl urea and their derivatives.

From the viewpoints such as the shelf life of the copying papers, the color tone of the developed color and the color density of the copied images, the employment as the alkaligenerating agent of trichloro acetate is most desirable.

Furthermore, the thiourea and its derivatives which can be applied to the present invention are those which are expressed by the following general formula:

Wherein: R and R are selected from the group consisting of H, alkyl radicals having 1 to 3 carbon atoms, acyl radicals, phenyl radical and benzoyl radical.

Those compounds which are expressed by the aforesaid general formula include:

Thiourea m.p. l76'l78C. 1.3-dimethyl thiourea m.p. 59 C. 1.3-dicthyl thiourea m.p. 79 C. l-allyl-Z-thiourea m.p. 72 C. l-allyl-Z-B-hydroxyethyl thiourea m.p. 77 C. l-acctyl thiourea m.p. l67 C. l-phcnyl thiourea m.p. l50 C. l-bcnzoyl thiourea m.p. 177 C.

The metal sulfates which are used jointly with the aforesaid thiourea and its derivatives in the present invention are selected from the group consisting of manganese sulfate, magnesium sulfate, nickel sulfate, zinc sulfate, cadmium sulfate and aluminum sulfate.

When a copying paper containing such a metal sulfate in its light-sensitive layer is developed at a temperature which is close to the decomposition temperature of the thiourea or its derivatives, the aforesaid metal sulfate will be inevitably brought into reaction with the sulfur which is isolated from a part of the thiourea or its derivative which is decomposed by the heat and, as a result, there will be produced a metal sul fide. This metal sulfide, however, is liable to stain the copy which carries an image developed thereon. For example, cadmium sulfide which bears a yellow color affects the expected tone of the color which is developed on the copying paper. Likewise, nickel sulfide will add its blackish color element to the expected color tone, while manganese sulfide which bears a greenish color will stain the expected color tone of the copied image by introducing a greenish color element thereto. By taking the aforesaid fact in consideration, it will be understood that the employment as the metal sulfate of magnesium sulfate or zinc sulfate which gives rise to the for mation of a metal sulfide bearing a white color is most suitable.

As will be clearly understood from the foregoing statement, the light-sensitive layer of the thermographic diazo-type copying paper which is provided according to the present invention contains thiourea or a derivative thereof and also a metal sulfate, in addition to the four basic components which consist of a diazo compound, a coupler, an acid stabilizer and an alkali-generating agent. The amount of the thiourea or a derivative thereof which is included in 1100 g. of the mixed solution which is to be coated on the support paper in the manufacture of a thermographic copying material is in the range of from about 3 g. to about 15 g. The amount of the metal sulfate which is included in g. of the mixed solution is in the range of from about 1 g. to about 8 g. and preferably, it is about one half of the amount of the thiourea or its derivative which is contained in said solution.

While the thermographic copying paper of the present invention contains in its light Sensitive layer thiourea or a derivative thereof and a metal sulfate, it is to be noted that the thiourea or its derivatives which are of a limited reducing property will also display an effect as being an antioxidizing agent. The presence of thiourea or its derivates in the light-sensitive layer will accordingly contribute to the protection of the background of the developed copy from being stained due to the possible oxidation of the latter. This fact leads to the improvement against fading of the developed color or the copy during its storage. The metal sulfate which is included in the light-sensitive layer, on the other hand, is considered to be present therein in the state of a complex salt which is formed with said thiourea or its derivate. However, the presence of the metal sulfate in the light-sensitive layer provides the advantages that the shelf life of the copying paper per se is enhanced and also that the clarity of the copied image is improved and further that the fastness of the copy is increased.

DESCRlPTION OF THE PREFERRED EMBODIM ENTS Example 1 A light-sensitive solution having the following composition:

p-dimethyl aminobenzene diazonium chloride zinc was applied uniformly onto one surface of a support paper in an amount ranging from 30 to 60 g./m., with the result that a thermographic diazo-type copying paper having a highly improved shelf life was obtained. By exposing this copying paper to ultraviolet rays through an original placed on the light-sensitive layer thereof to form thereon a latent image, and thereafter by developing the same by bringing the copying paper into contact with a hot roller heated so as to have a surface temperature of C. for about 6 seconds, a clear blue copied image was obtained. In case said magnesium sulfate was omitted from the aforesaid composition of the solution, the resulting copying paper gave a blue copied image, but the shelf life of this copy deteriorated to such an extent that it was not suitable for actual use. Saponin was contained in the aforementioned composition so as to serve as a surface active agent which was effective in the accomplishment of the uniform application of the light-sensitive solution throughout the surface of the support paper.

Example 2 2 By using a light-sensitive solution having the following com position:

p-morpholino-2,5-dimethoxy-benzene diazonium Example 3 A mixed solution having the following composition:

p-diethylamino-benzene diazonium chloride zinc chloride double salt 1.1 g.

2,7-dihydroxy-naphthalene-3,o-disulfonate sodium 4.0 g. Citric acid 1.0 g. Potassium trichloro acetate 5.0 g. l,3-dimethyl thiourea 8.0 g. Cadmium sulfate 3.5 g. Naphthalene trisulfonate sodium 2.5 g. Saponin 0.] g. Water 100 g.

was applied uniformly onto one surface of a support paper and was dried in the same manner as that described in example 1, and thus thermographic diazotype copying paper was prepared. This copying paper was then exposed to ultraviolet rays through an original placed on the light-sensitive layer thereof, and by thereafter heating the exposed copying paper at 170 C. for 8 seconds, a clear copied image of blue in color and having a highly increased color density was obtained. This copy had a greatly improved shelf life.

EXAMPLE 4 By using a mixed solution having the following composition:

p-morpholino-2,S-diethoxy benzene diazonium chloride -zinc chloride double salt l.5 g. l-hydroxy-4-sodium sulfonate naphthalene 4.0 g. Ouanidine trichloro acetate 3.0 g.

Tartaric acid 0.5 g. l-allyl-2-thiourea 5.0 g. Zinc sulfate 2.0 g. Naphthalene trisulfonate sodium L5 Saponin 0.l g. Water g.

in the same manner as that described in example 1, a thermographic diazotype copying paper was prepared. After exposing this copying paper to light, the latter was heated at C. for 8 seconds. As a result, a clear copied image of bluish violet in color was obtained.

What is claimed is:

l. A thermographic diazo-type copying material, comprising a support having one surface coated with a light sensitive coating composition containing a. a diazonium compound b. an azo coupling component c. an acid stabilizer d. a thermally decomposable alkali-generating agent selected from the group consisting of the sodium, potassium, alkyl amine (in which the alkyl has 1 to 4 carbon atoms), guanidine, aminoguanidine, benzoylguanidine, guanyl urea and biguanide salts of trichloroacetic acid,

e. a compound selected from the group consisting of thiourea and its derivatives and having the formula RNH-(IJNHR in which R and R are selected from the group consisting of H, alkyl and alkenyl radicals having up to 3 carbon atoms and their corresponding acyl radicals, phenyl radical and benzoyl radical, and

f. a metal sulfate selected from the group consisting of magnesium sulfate and zinc sulfate, said thiourea and its derivatives is present in the said composition in the amount of from about 3 to about 15 gr. and said metal sulfate is present in the said composition in the amount of from about 1 to about 8 gr. per 100 gr. of the mixed solution including solvent applied to said support to form coating composition.

2. A thermographic diazotype copying material according to claim 5, wherein the amount of said metal sulfate in said composition is about one half the amount of said compound selected from the group consisting of thiourea and its derivatives. 

2. A thermographic diazotype copying material according to claim 5, wherein the amount of said metal sulfate in said composition is about one half the amount of said compound selected from the group consisting of thiourea and its derivatives. 